Low-voltage high-speed receiver

ABSTRACT

A line receiver is described. The line receiver may be configured to receive signals transmitted via a communication channel, such as a metal trace on a printed circuit board or a cable. The receiver may comprise a buffer and circuitry for enhancing the trans-conductance gain of the buffer. By enhancing the trans-conductance gain of the buffer, linearity may be improved and susceptibility to process and temperature variations may be limited. Enhancement of the trans-conductance gain may be performed using feedback circuitry coupled to the buffer. The receiver may further comprise mirror circuitry configured to provide a desired current to the load. The receiver may further comprise a gain stage for setting the gain of the receiver to a desired level.

RELATED APPLICATIONS

This Application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser. No. 62/372,336, entitled “LOW-VOLTAGE HIGH-SPEED RECEIVER” filed on Aug. 9, 2016, which is herein incorporated by reference in its entirety.

BACKGROUND

Line receivers are used in electronics to receive signals transmitted through transmission lines. Types of line receivers include voltage mode drivers and current mode drivers.

BRIEF SUMMARY

According to one aspect of the present application, a line receiver is provided. The line receiver may comprise a buffer configured to receive an input signal, the buffer having a first transconductance gain, feedback circuitry coupled to the buffer and configured to provide a second transconductance gain greater than the first transconductance gain, mirror circuitry coupled to the buffer and configured to generate a current in response to receiving an intermediate signal from the buffer, and a gain stage configured to receive the current and to generate an output signal.

In some embodiments, the current is a first current that is substantially equal to a second current in the buffer.

In some embodiments, the buffer comprises a transistor arranged in a source-follower configuration.

In some embodiments, the transistor is a first transistor and wherein the feedback circuitry further comprises a second transistor coupled to the first transistor and arranged in a common-source configuration.

In some embodiments, the feedback circuitry further comprises an impedance element coupled between a gate terminal of the second transistor and a drain terminal of the first transistor.

In some embodiments, the intermediate signal comprises a voltage of a gate terminal of the second transistor.

In some embodiments, a source terminal of the first transistor is coupled to a drain terminal of the second transistor.

In some embodiments, the line receiver further comprises an impedance element coupled to the source terminal of the first transistor.

In some embodiments, the buffer further comprises a third transistor having a drain terminal coupled to a drain terminal of the first transistor.

In some embodiments, the gain stage comprises a plurality of transistors configured to provide an adjustable gain.

In some embodiments, the minor circuitry comprises a transistor arranged in a common source configuration.

In some embodiments, the gain stage comprises a load coupled to a drain terminal of the transistor.

In some embodiments, the buffer is not configured to withstand supply voltages greater than 1V.

In some embodiments, the buffer comprises a first transistor arranged in a source-follower configuration, the feedback circuitry comprises a second transistor coupled to the first transistor and arranged in a common-source configuration and the mirror circuitry comprises a third transistor arranged in a common-source configuration, wherein the second transistor and the third transistor are configured to receive a common gate/source voltage.

According to another aspect of the present application, a method is provided. The method may comprise receiving an input signal with a buffer having a transconductance gain, amplifying the transconductance gain of the buffer with feedback circuitry coupled to the buffer, generating a current in response to receiving, with minor circuitry, an intermediate signal from the buffer, and generating, with a gain stage, an output signal in response to receiving the current.

In some embodiments, the current is a first current, and wherein generating the first current comprises minoring a second current in the buffer.

In some embodiments, amplifying the transconductance stage with the feedback circuitry comprises biasing a plurality of transistor with an impedance element.

In some embodiments, generating the output signal comprises providing an adjustable gain by selecting at least one among a plurality of drive transistors.

In some embodiments, the method further comprises setting a frequency response by setting a value for an impedance element coupled to the buffer.

In some embodiments, the method further comprises supplying the buffer with a supply voltage that is less than 1V.

The foregoing summary is provided by way of illustration and is not intended to be limiting.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing.

FIG. 1 is a block diagram illustrating a communication system, according to some non-limiting embodiments;

FIG. 2 is a circuit diagram illustrating a line receiver comprising a plurality of transistors, according to some non-limiting embodiments;

FIG. 3 is a circuit diagram illustrating a line receiver configured to provide an adjustable gain, according to some non-limiting embodiments;

FIG. 4 is a circuit diagram illustrating a line receiver configured to operate differentially, according to some non-limiting embodiments;

FIG. 5 is a circuit diagram illustrating another line receiver configured to operate differentially, according to some non-limiting embodiments.

DETAILED DESCRIPTION

The inventors have recognized a challenge in the design of line receivers that has risen as the size of integrated transistors decreases (e.g., as the complementary metal-oxide-semiconductor (CMOS) fabrication node decreases). Smaller transistors are less able to handle the voltage stresses, thus limiting the maximum voltage with which a circuit including such transistors can be supplied. As a result of this reduction in the supply voltage, the linearity of the line receivers is degraded. One of the reasons for such degraded linearity is the difficulty of biasing transistors in the linear region (e.g., a field effect transistor's saturation region or a bipolar transistor's active region) with a low supply voltage (e.g., less than 1V).

To overcome this limitation, some conventional line receivers utilize multiple signal buffers connected in series. The buffers, which provide a high input impedance and a low output impedance, are configured to operate at low supply voltages. However, the use of multiple buffers poses serious limitations on linearity, as well as on power consumption and sensitivity to process and temperature variations. Furthermore, some conventional types of buffers, such as current mode logic (CML) drivers, do not provide means for independently controlling the gain from the frequency response. As a result, increasing the line receiver's gain will cause a decrease in the bandwidth of the line receiver, or vice versa. Therefore, designers of line receivers may have to make design compromises.

Other conventional line receivers deal with the inability of small transistors to tolerate large supply voltage by separating a die into two portions: one portion includes an analog circuit configured to receive a high supply voltage (e.g., equal to or greater than 1V), and the other portion includes a digital circuit configured to receive a low supply voltage (e.g., lower than 1V). Due to the larger supply voltage received, the analog circuit provides the desired level of linearity. On the other hand, due to the lower supply voltage, the digital circuit can process digital signals without incurring stress. While this solutions provides the desired linearity, supplying a receiver with multiple voltages may be undesirable due to the added complexity.

The inventors have developed line receivers, also referred to herein simply as receivers, that can provide the linearity desired while overcoming at least some of the drawbacks of prior solutions. In particular, the inventors have appreciated that linearity can be increased by increasing the trans-conductance gain of the buffer used to receive input signals. In some embodiments, the trans-conductance gain may be increased by providing a feedback circuit coupled to the buffer. In this way, the resulting trans-conductance gain may be proportional to the product of the trans-conductance gain of the buffer and the trans-conductance gain of the feedback circuit. In some embodiments, to further increase the trans-conductance gain, the feedback circuit may be coupled to a node having a high impedance.

The inventors have further appreciated that by increasing the trans-conductance gain of the buffer, the line receiver's sensitivity to temperature and process variations may be mitigated. In fact, in some embodiments, a larger trans-conductance gain may result in the line receiver having a gain that depends mainly on passive components (e.g., resistors). Compared to active components (e.g., transistors), the characteristics of passive components are less prone to fluctuations caused by temperature and process variations. As a result, gains that mainly depend on passive components may also experience less fluctuations. In some embodiments, in order to provide a gain that depends mainly on passive components, a mirror circuit may be used. The mirror circuit may be coupled to the feedback circuit and may have a trans-conductance gain that substantially matches (e.g., is within 75% and 125%, within 90% and 110%, within 95% and 105%, or within 99% and 101%) the trans-conductance gain of the feedback circuit. In this way, the current flowing in the load, and a result the gain of the line receiver, may be substantially independent from active components.

FIG. 1 is a block diagram illustrating an example of a communication system, according to some non-limiting embodiments. Communication system 100 may comprise a transmitter 101 and a receiver 102. The transmitter 101 may be electrically coupled to the receiver 102 via a communication channel, such as cable (e.g., a twinax or a coax) and/or a metal trace on a printed circuit board. Alternative types of communications channels may be used. Transmitter 101 may be configured to transmit data at more than 10 Gb/s, more than 20 Gb/s, more than 30 Gb/s, more than 40 Gb/s, more than 50 Gb/s, or more than any other suitable value. In some embodiments, transmitter 101 may operate between 40 Gb/s and 80 Gb/s, or within any range within such range.

Receiver 102 may be configured to receive signals transmitted by transmitter 101 through the communication channel. In some embodiments, receiver 102 may include buffer 104, feedback circuitry 106, mirror circuitry 108 and gain stage 110. Buffer 104 may be configured to receive the signal provided by transmitter 101. In some embodiments, buffer 104 has a large input impedance (e.g., more than 100KΩ, more than 500 KΩ, or more than 1MΩ), and a small output impedance (e.g., less than 1KΩ, less than 100Ω, or less than 10Ω). In this way, buffer 104 may operate as an impedance transformer, thus preventing the load from loading the buffer excessively. In some embodiments, buffer 104 may be implemented using a source follower.

Feedback circuit 106 may be coupled to buffer 104 in any suitable way. In some embodiments, feedback circuitry 106 may be coupled between the output terminal of buffer 104 and a node of buffer 104 having a large impedance (e.g., more than 5KΩ, more than 50 KΩ, or more than 100KΩ). In other embodiments, feedback circuitry 106 may be coupled between the input and output terminals of buffer 104. Feedback circuitry 106 may be configured to increase the trans-conductance gain of buffer 104 by any suitable amount. For example, the trans-conductance gain may be increased by a factor between 1 and 1000, between 1 and 100, between 1 and 10, between 10 and 100, between 100 and 1000, or between any values between such ranges. In some embodiments, the multiplication factor may be proportional to the trans-conductance gain of feedback circuitry 106. Feedback circuitry 106 may be configured to bias buffer 104. For example, feedback circuitry 106 may be configured to bias buffer 104 in a linear region (e.g., in a saturation region if buffer 104 is implemented using field effect transistors or in an active region if buffer 104 is implemented using bipolar transistors).

Mirror circuitry 108 may be coupled to buffer 104 and/or feedback circuitry 106 in any suitable way. In some embodiments, mirror circuitry 108 may share one or more terminals with feedback circuitry 106. In some embodiments, the mirror circuit may have a trans-conductance gain that substantially matches (e.g., is within 75% and 125%, within 90% and 110%, within 95% and 105%, or within 99% and 101%) the trans-conductance gain of the feedback circuitry. The mirror circuitry may be used to generate a current substantially matching a current flowing in an impedance element of buffer 104. As will be described further below, in this way the current provided by mirror circuitry 108 may mainly depend on passive components (e.g., resistive elements).

Gain stage 110 may comprise a load. The load may comprise a resistive element in some embodiments. The resistive element may be implemented in any suitable way, including a resistor and/or an active load. Resistors may be implemented using a doped region of semiconductor material having a size designed to provide a desired resistance. The load may receive the current generated by mirror circuitry 108. In some embodiments, gain stage 110 may comprise circuitry for adjusting the amount of current flowing in the load. In some such embodiments, gain stage 110 may comprise a plurality of drivers connected in parallel. The drivers may be turned on/off to provide a desired output current, and thus a desired gain.

The receiver illustrated in FIG. 1 may be implemented using transistors in some embodiments. The transistors may be fabricated on a monolithic substrate using semiconductor fabrication techniques. In some embodiments, the transistors may comprise field effect transistors, such as metal oxide semiconductor field effect transistors (MOSFET), or junction field effect transistors (JFET). In other embodiments, the transistors may comprise bipolar transistors, such as bipolar junction transistors (BJT). In yet other embodiments, hybrid configuration may be used. In some embodiments, the transistors may be fabricated using a fabrication node that is less than 14 nm, less than 12 nm, less than 10 nm, less than 8 nm, or less than 6 nm. Due to their size, the resulting transistors may be configured to receive supply voltages that are less than a certain threshold (e.g., less than or equal to 1.2V, less than or equal to 1.1V, less than or equal to 1V, less than or equal to 0.9V, less than or equal to 0.8V, less than or equal to 0.7V, less than or equal to 0.6V, less than or equal to 0.5V, or less than any suitable value). If the transistors receive supply voltages that are larger than the threshold, they may experience stress and as a result may be damaged.

FIG. 2 is a circuit diagram illustrating a receiver comprising a plurality of transistors, according to some non-limiting embodiments. Receiver 200 may comprise buffer 204, which may serve as buffer 104 of FIG. 1. Buffer 204 may comprise a source follower in some embodiments. For example, buffer 204 may comprise transistor M₂, which may be arranged in a common-drain configuration. In some embodiments, transistor M₂ may be an NMOS transistor. In some embodiments, transistor M₂ may have a gate terminal coupled to node “in”, a drain terminal coupled to node “H”, and a source terminal coupled to node “L”. Transistor M₂ may receive input signals provided by transmitter 101 via node “in”. In response, transistor M₂ may provide a voltage at node “L”. In some embodiments, transistor M₂ may exhibit a substantially unitary voltage gain. As a result, the voltage V_(L) at node “L” may be substantially equal to the voltage V_(in) at node “in”. Transistor M2 may have a trans-conductance gain g_(m2) that is between 1 mΩ⁻¹ and 100 mΩ⁻¹, when biased in the saturation region

In some embodiments, buffer 204 may comprise an impedance element. The impedance element may be coupled to source terminal of transistor M₂. In some embodiments, the impedance element may comprise a resistive element. For example, the impedance element may comprise resistor R_(D). In some embodiments, the impedance element may comprise a capacitive element. For example, the impedance element may comprise capacitor C_(Peaking). In some embodiments, C_(Peaking) may be a variable capacitor (e.g., a varactor). In some embodiments, by varying the capacitance associated with capacitor C_(Peaking) and/or the resistance associated with resistor R_(D), the frequency response of buffer 204, and as a result of receiver 200, may be varied. For example, by varying at least one, or both, of such parameters, the cut-off frequency (e.g., the 3 dB-frequency) of buffer 204 may be varied.

In some embodiments, buffer 200 may comprise transistor M₃. Transistor M₃ may be coupled to transistor M₂ in any suitable way. For example, transistor M3 may have a drain terminal coupled to the drain terminal of transistor M₂, a source terminal coupled to a supply voltage V_(DD), and a gate terminal configured to receive a voltage V_(b). Supply voltage V_(DD) may be less than 1V in some embodiments. In some embodiments, voltage V_(b) may be configured to place transistor M₃ in saturation. Transistor M₃ may be coupled to transistor M₂ in an arrangement that provides a high impedance at node “H” (e.g., more than 5KΩ, more than 50KΩ, or more than 100KΩ). In some embodiments, being node “H” connected to the drain of transistor M₃, its impedance may be proportional to the drain resistance of transistor M₃.

The inventors have appreciated that if the load of receiver 200 was to be coupled to the output terminal of buffer 204 (e.g., the terminal coupled to node “L”), the gain of the receiver would be proportional to the trans-conductance g_(m2) of transistor M₂. Because g_(m2) may fluctuate in response to process and temperature variations, the gain of receiver 200 may also exhibit fluctuations. This situation may be undesirable as it may produce noise on the output signal. In addition, the linearity of receiver 200 may be limited by the low supply voltage available. Accordingly, when a low supply voltage is provided, biasing transistors M₂ and M₃ in saturation may be challenging,

To obviate these problems, feedback circuitry 206 may be used. Feedback circuitry 206 may serve as feedback circuitry 106 of FIG. 1. Feedback circuitry 206 may comprise one or more transistors in some embodiments. For example, feedback circuitry 206 may comprise transistor M₁, which may be an NMOS transistor. Transistor M₁ may be coupled to buffer 204 in any suitable way. For example, transistor M₁ may comprise a drain terminal coupled to the source terminal of transistor M₂, a source terminal coupled to a reference terminal (e.g., a ground terminal), and a gate terminal coupled to the drain terminal of transistor M₂.

In some embodiments, to guarantee that transistors M₁, M₂ and M₃ are biased in the saturation region at the same time, the gate terminal of transistor M1 may be coupled to the drain terminal of transistor M2 via a feedback impedance element. The feedback impedance element may configured to provide a desired voltage drop between its terminals, thus providing a desired bias voltage to transistors M₁, M₂ and M₃. In this way, the transistors may be biased in the saturation region simultaneously, thus improving the linearity of receiver 200. In some embodiments, the feedback impedance element may comprise a resistive element, such as resistor R_(F). In some embodiments, the feedback impedance element may comprise a capacitive element, such as capacitor C_(F). The capacitor C_(F) may be variable in some embodiments. Having a variable capacitor may be desirable as it may be used to adjust the bandwidth of the receiver as appropriate. Current generator I₀ may be coupled to node “X”. In this configuration, the overall trans-conductance gain of the buffer coupled to the feedback circuitry may be significantly increased. For example, in some embodiments, the overall trans-conductance gain may be given by:

g _(m) ^(boosted) =g _(m2)(1+g _(m1) r ₀)

where g_(m2) is the trans-conductance of transistor M₂, g_(m1) is the trans-conductance of transistor M₁, and r₀ is the impedance at node “H”.

When an input voltage V_(in) is received at node “in”, the intermediate voltage V_(x) at node “X” may be given by the following expression:

V _(x) =−V _(in)(g _(m2) r ₀)/(1+R _(D) g _(m) ^(boosted))=−V _(in)(g _(m2) r ₀)/(1+R _(D) g _(m2)(1+g _(m1) r ₀))

If the product (g_(m1) r₀)>>1 (e.g., more than 10), then V_(x) may be approximated by

V _(x) =−V _(in)(g _(m2) r ₀)/(1+R _(D) g _(m2) g _(m1) r ₀)

If the product (R_(D) g_(m2) g_(m1) r₀)>>1 (e.g., more than 10), then V_(x) may be approximated by

V _(x) =−V _(in)/(R _(D) g _(m1))

Mirror circuitry 208 may serve as mirror circuitry 108 of FIG. 1. In some embodiments, mirror circuitry 208 may be configured to receive voltage V_(x), and to provide a current that is substantially independent of g_(m1). In some embodiments, mirror circuitry 208 may comprise transistor M₄, which may be coupled to feedback circuitry 206 in any suitable way. For example, transistor M₄ may comprise a source terminal coupled to the source terminal of transistor M₁, and a gate terminal coupled to the gate terminal of transistor M₁. In this way, transistors M₁ and M₄ may have the same gate-source voltage, and as a result the same trans-conductance gain. In response to receiving V_(x), transistor M₄ may generate a current i₀ flowing between its source and drain terminals. The current i₀ may be given by

i₀=−g_(m4) V_(x)

where g_(m4) is the trans-conductance gain of transistor M₄. In the embodiments in which g_(m4)=g_(m1), the current may be given by

i ₀ =−g _(m4) V _(x) =−g _(m1) V _(x) =V _(in) /R _(D)

As shown, the current may be substantially equal (e.g., between 75% and 125%, between 90% and 110%, between 95% and 105%, or between 99% and 101%) to the current flowing in the resistor R_(D).

Gain stage 210 may serve as gain stage 110 of FIG. 1. Gain stage 210 may comprise a load in some embodiments. The load may comprise a resistive element, such as resistor R_(L). The load may be coupled to mirror circuitry 208 in any suitable way. For example, resistor R_(L) may be coupled to the drain terminal of transistor M₄. The ac voltage V_(out) at node “out” may be given by i₀ R_(L)=(V_(in) R_(L))/R_(D). As a result, the gain of receiver 200 may be equal to A_(v)=V_(out)/V_(in)=R_(L)/R_(D). As shown, the gain may mainly depend on a resistance ratio, and therefore may be substantially insensitive to process and temperature variations. It should be appreciated that the gain and the frequency response of receiver 200 may be controlled independently of each other. The frequency response of the receiver may be adjusted by varying the value of the capacitance of capacitor C_(Peaking) and/or the value of the resistance of resistor R_(D). While variations in R_(D) may also vary the gain of receiver, also variations in R_(L) may vary the gain of receiver. Therefore, by setting desired values for R_(D) and R_(L), the gain and the frequency response may be independently set.

In some embodiments, gain stage 210 may comprise a transistor configured to operate as a switch. For example, transistor M₅ may be coupled between transistor M₄ and the load. Transistor M₅ may allow/inhibit current i₀ from reaching the load. For example, depending on the voltage of the signal at its gate terminal, transistor M₅ may be placed in an on-state (a conductive state) or an off-state (a high impedance state).

In some embodiments, the gain of a receiver may be alternatively, or additionally, controlled by controlling the current flowing through the load. FIG. 3 is a circuit diagram illustrating a receiver configured to provide an adjustable gain, according to some non-limiting embodiments. Receiver 300 may comprise a plurality of transistors M₄ and a plurality of transistors M₅. Each of the plurality of transistors M₄ may have a source terminal coupled to the source terminal of transistor M₁, and a gate terminal coupled to the gate terminal of transistor M₁. In this way, each of the plurality of transistors M₄ may have substantially the same trans-conductance gain as transistor M₁. Each of the plurality of transistors M₅ may have a source terminal coupled to a drain terminal of a respective transistors M₄. In this way, each transistor M₅ may receive a current i₀.

The state of transistors M₅ may be controlled by using a plurality of control signals S₁, S₂ . . . S_(n). The control signals may be configured to place a respective transistor M5 in an on-state or an off-state. In this way, the amount of current flowing through the load may be controlled, and may depend on the number of transistors M₅ that are in an on-state. As a result, the gain of receiver 300 may be adjusted as desired.

FIGS. 2-3 illustrate receivers arranged to operate in a single ended configuration. However, it should be appreciated that receivers of the type described herein may alternatively be arranged to operate differentially. In some embodiments, a differential receiver may include more than one single ended receiver, such as receiver 200 or 300. FIG. 4 is a circuit diagram illustrating a receiver configured to operate differentially, according to some non-limiting embodiments. Receiver 400 may include a pair of receivers 300. Receiver 400 may be configured to receive a differential input signal, such as V_(im)-V_(ip), and to produce a differential output signal, such as V_(om)-V_(op). The amplitude of the output signal may depend on the gain provided by the receivers 300.

Receiver 400 may comprise circuit elements configured to control the common mode output signal. For example, receiver 400 may comprise resistors R_(L), amplifier 402 and transistors M₁₀ and M₁₁. Such circuit elements may be configured to detect the common mode associated with the output signal, and to set the common mode to a desired level. For example, the common mode may be set to a predefined value, which may be independent from the selected gain. In the example illustrated in FIG. 4, the common mode may be sensed at node “K”, and may be compared to a reference common mode voltage V_(CM,ref), using amplifier 402. Being arranged in an open loop configuration, amplifier 402 may operate as a comparator. In some embodiments, if the voltage at node “K” is greater than V_(CM,ref), amplifier 402 may output a voltage which may set transistors M₁₀ and M₁₁ in an off-state. In contrast, if the voltage at node “K” is less than V_(CM,ref), amplifier 402 may output a voltage which may set transistors M₁₀ and M₁₁ in an on-state. The opposite logic may alternatively be used in other embodiments. Being coupled to the output terminals of receiver 400, transistors M₁₀ and M₁₁ may close the feedback loop thus setting the common mode of the output signal to V_(CM,ref). Being V_(CM,ref) independent from the gain, distortion to the output signal may be limited.

While FIG. 4 illustrates resistors R_(D) and capacitors C_(peaking) as being connected between node “L” and the ground terminal, other configurations are also possible. For example, in some embodiments, resistor R_(D) and capacitor C_(peaking) may be connected between the differential nodes, as illustrated in FIG. 5.

Various aspects of the apparatus and techniques described herein may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing description and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments.

Use of ordinal terms such as “first”, “second”, “third”, etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including”, “comprising”, “having”, “containing” or “involving” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

The use of “coupled” or “connected” is meant to refer to circuit elements, or signals, that are either directly linked to one another or through intermediate components. 

What is claimed is:
 1. A line receiver comprising: a buffer configured to receive an input signal, the buffer having a first transconductance gain; feedback circuitry coupled to the buffer and configured to provide a second transconductance gain greater than the first transconductance gain; mirror circuitry coupled to the buffer and configured to generate a current in response to receiving an intermediate signal from the buffer; and a gain stage configured to receive the current and to generate an output signal.
 2. The line receiver of claim 1, wherein the current is a first current that is substantially equal to a second current in the buffer.
 3. The line receiver of claim 1, wherein the buffer comprises a transistor arranged in a source-follower configuration.
 4. The line receiver of claim 3, wherein the transistor is a first transistor and wherein the feedback circuitry further comprises a second transistor coupled to the first transistor and arranged in a common-source configuration.
 5. The line receiver of claim 4, wherein the feedback circuitry further comprises an impedance element coupled between a gate terminal of the second transistor and a drain terminal of the first transistor.
 6. The line receiver of claim 4, wherein the intermediate signal comprises a voltage of a gate terminal of the second transistor.
 7. The line receiver of claim 4, wherein a source terminal of the first transistor is coupled to a drain terminal of the second transistor.
 8. The line receiver of claim 7, further comprising an impedance element coupled to the source terminal of the first transistor.
 9. The line receiver of claim 7, wherein the buffer further comprises a third transistor having a drain terminal coupled to a drain terminal of the first transistor.
 10. The line receiver of claim 1, wherein the gain stage comprises a plurality of transistors configured to provide an adjustable gain.
 11. The line receiver of claim 1, wherein the mirror circuitry comprises a transistor arranged in a common source configuration.
 12. The line receiver of claim 11, wherein the gain stage comprises a load coupled to a drain terminal of the transistor.
 13. The line receiver of claim 1, wherein the buffer is not configured to withstand supply voltages greater than 1V.
 14. The line receiver of claim 1, wherein the buffer comprises a first transistor arranged in a source-follower configuration, the feedback circuitry comprises a second transistor coupled to the first transistor and arranged in a common-source configuration and the mirror circuitry comprises a third transistor arranged in a common-source configuration, wherein the second transistor and the third transistor are configured to receive a common gate/source voltage.
 15. A method comprising: receiving an input signal with a buffer having a transconductance gain; amplifying the transconductance gain of the buffer with feedback circuitry coupled to the buffer; generating a current in response to receiving, with mirror circuitry, an intermediate signal from the buffer; and generating, with a gain stage, an output signal in response to receiving the current.
 16. The method of claim 15, wherein the current is a first current, and wherein generating the first current comprises mirroring a second current in the buffer.
 17. The method of claim 15, wherein amplifying the transconductance stage with the feedback circuitry comprises biasing a plurality of transistor with an impedance element.
 18. The method of claim 15, wherein generating the output signal comprises providing an adjustable gain by selecting at least one among a plurality of drive transistors.
 19. The method of claim 15, further comprising setting a frequency response by setting a value for an impedance element coupled to the buffer.
 20. The method of claim 15, further comprising supplying the buffer with a supply voltage that is less than 1V. 